Compound stops

Compound stops are combined from multipl rows of pipes per rank, to be further distinguished into several types like multiple fundamental ranks or aliquot ranks which sometimes repeat in itselves.

 A compound fundamental rank is „Bifara“, consisting of two 8’-pipes (often in one with two labia) on the slider or a doubling of string pipes  (south German, so with Gabler or Freywiß), diapasons or flutes (cf. Organ in Amsterdam). In a wider sense to those also belong undulating ranks- although usually with separate stops - like the typical italian undulating diapason „Voce umana“. other regions preferred undulating flute or string ranks. The specific undulating effect can only be achieved in combination with one rank of similar measures and length (usually  8’).

Since infrequently some organist were unfamiliar with the necessary combinations some organ maker have added specific advices like eg at the organ at Maihingen by Johann Martin Baumeister, who added to the undulating flute „Cythara“ 8’ the remark „mit der Flauten allein“ . Another option was a technical link like Heinrich Trost did in his organ in Waltershausen, where the Vox humana can only be played combined with  Hohlflöte 8’ but without effect alone or in other combinations. The specific make of such compound ranks thus is very characteristic for single makers or certain regions.

Aliquot ranks
The function of Aliquot ranks is a reinforcement of overtones with the generally poor labial ranks. Aliquotes were a favourite means to synthesize specific tone colours eg to simulate the sound of reed stops rich in overtones with labial stops poor in overtones only.  Mixture ranks are also compound ranks  usually adding more octaves and fifts'harmonics but of a different purpose, to add specific typical organ splendour.

Aspecific groups of mixed compound ranks is not repeating meaning the foot lengths stay the same over the compass, like the following with very few exceptions

Rauschpfeife 2f.:                               2²/₃’     +         2’        (harmonics 3+4 to 8’)
Sesquialtera 2f.:                                2²/₃’     +         1³/₅’   (harmonics 3+5 to 8’)
(variant:)
Sesquialtera 3f.:                                2²/₃’ + 2’ +     1³/₅’    (harmonics 3-5 to 8’)
Hörnl 2f.:                                            2’          +         1³/₅’   (harmonics 4+5 to 8’)
Terzian 2f.:                                         1³/₅’      +         1¹/₃’   (harmonics 5+6 to 8’)

Occasionally these ranks were built with not more than one repetition as follows in Sesquialtera:  in the lowest octave beginning on  1¹/₃’+⁴/₅’, changing on c to 2²/₃’+1³/₅’ to top.

Some ot these ranks were typical for certain regions: Rauschpfeife eg was common in Northern Germany, the triple  Sesquialtera a characterism for some organ makers in the west of Germany, Hörnl specific for souther Germanic alpine regions.

Another specific compound rank is the typical French (but following this pattern widely beyond);

Cornet/Recit 8’ 5f.:                           8’+4’+2²/₃’+2’+1³/₅’  (harmonics 1+2+3+4+5)

as a special solo stop. Some malers made it only fourfold ( without a fixed 8’) or threefold (without 8’ and 4’), to enable a certain choice for the player what fundament to combine. If the Cornet was complete ie fivefold, the 8’ usually was a stopped or Rohrflöte, the 4’ a diapason The Cornet 5f. was usually a treble stop only (from c¹).

Unlike the above mentioned the mixtures usually repeat several times These are including the common mixtur also Scharf and Zimbel, usually with regional differences. Common is traditionally  a combination of octavens and fifths above the fundamental (harmonics 2/4/8/16... resp. 3/6/12..., either singles or doubled). During the 18th c.  some organ builders also integrated thirds into mixtur;  later called „Scharf“, although this rank usually contained no thirds.

Older traditions separated these according to highness: mixtur had lower ranks than Scharf, this had lower than Zimbel (in relation to the fundamental). If Mixtur on C had 2’ (+1¹/₃’+1’ ...; harmonic 4/6/8 ff.),  Scharf began on 1’ (+²/₃’+¹/₂’ ...; harmonics 8/12/16 ff.) and Zimbel on ½’ (+¹/₃’+¹/₄’; harmonics 16/24/32).

But this could not be extended over the complete compass: On C the peak of such a Zimbel was c⁴. Wih an assumed top note of c³ on this fundamental had required a c⁸ with a pipe length of ¹/₆₄’ equalling roughly 4 mm – not only difficult to build, let alone to tune, this note is outside the human hearing range anyway.

The  „Repetition“ of these ranks involves that every one of these ranks „breaks“ at a certain top  (mostly c⁵ equalling ¹/₈’, the „Plafond“/the top limit of an organ) to be shifted one octave lower.

 Ex,: Zimbel 3f. initially: ½’+¹/₃’+¹/₄’ to fundament: